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Not just another option to tick or leave when buying a new car. ABS - or anti-lock braking system - is one of the most effective active safety devices available. The idea is to stop a car's wheels locking up during braking, because a skidding wheel has less retardation ability and (if it's on a front wheel) does not allow steering control. Sensors on the wheel detect lock-up - when it stops rotating - and a microprocessor tells the brakes to ease-off and reapply many times each second to achieve optimum braking. All the driver has to do is jam on the brake pedal but beware: stopping distances on slippery roads will still be greater than in the dry. Similarly, ABS will not control a front- or rear-wheel slide, meaning the car can still spin.

Active Steering

Active steering can alter the steering ratio depending on the speed of the car or how it is being driven. For example, at higher speeds active steering technology will require more input to turn the wheels, in order to lessen the twitchiness of the car and provide a more stable feel. At lower speeds, when parking the car for example, active steering will allow the driver to turn the wheels from full left-lock to full right-lock without taking their hands off the wheel. Adaptive Headlights

Some luxury cars offer adaptive headlights - also known as cornering beams -and it basically means that the headlights will turn the corner with the driver. As you turn, the lights will alter the direction of the beam according to sensors that monitor steering angle and speed.

ANCAP

The Australasian New Car Assessment Program is one of the world's most authoritative independent crash test organisations. Car makers conduct hundreds of real and virtual crash tests when designing cars, but they don't release the data publically. ANCAP - and other international partners such as Euro NCAP - conduct their own crash tests and rate cars out of five stars. The NCAP formula has been criticised for encouraging specific vehicle design that works well in the laboratory crash test but may not perform as well in other real world crash tests. The rating critieria and tests are also evolving, so it's often difficult to compare cars tested only a few years ago with models tested more recently.

Airbags (SRS)

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We all have an image of airbags being soft, billowy pillows that save our lives in accidents, but have a think about this little experiment. Have someone hold a pillow against your bedroom wall and then run full tilt at it - that's about 25km/h for a self-propelled human - and smash your face into the pillow. Double the pain if the speed was 50km/h. That's about how much effect an airbag has in a car crash if a seatbelt hasn't already slowed your progress - and who drives at 50km/h anyway? So an airbag is a Supplementary Restraint System (SRS), not a replacement for seatbelts or deformable structures in cars. There are many different types of airbags fitted to new cars, and the range is ever-increasing. There are two broad categories of airbags: frontal and side-impact. Frontal airbags are located in front of the driver and/or passenger and will be activated by sensors and deployed in the instance of a collision. Frontal airbags include steering wheel, dash, and knee airbags. Side-impact airbags are designed to protect the driver and/or passengers in the event of a side-impact collision. Curtain airbags are considered some of the most important in reducing injuries; they protect the head in a side impact by inflating an air-filled cushion along the length of the car. Interestingly, some motorcycles offer airbag protection, and there are also motorcycle airbag suits available.

Alloy wheels

Most car wheels are pressed from thick sheets of steel, but alloys are cast from a variety of metals including magnesium, which is why dudes from the 1970s may still call them mags. All being well, alloys should be lighter, which allows the suspension to work better, and stronger to cope with cornering forces of sports cars. But most people buy them simply because they look better than conventional steel wheels.

Aqua planing

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Often misinterpreted as a slide or skid on a wet road, aqua planing is subtly different - and more difficult to control. Like a boat that gets up on the plane - or skips across the surface of the water rather than plowing through it - aqua planing refers to a condition whereby the tyres temporarily lose contact with the road. It occurs when water is standing on the road or running across it and the speed of the vehicle is too high to carve through the water to the road surface. Wider tyres or tyres with little or no tread left are more prone to aqua planing, as are light weight cars. When a car aqua planes the only chance of regaining control is when the wheels finally come back into contact with the road. The best way to avoid it is to slow down through puddles, small rivers across the road or standing water.

Auto start/stop

Fitted to some cars is a function that is called auto-start/stop. As its name suggests, the system can automatically shut the car down when it's stationary then automatically re-fire the engine when the driver presses the accelerator. Early systems aren't perfect and can be clunky in their restart, but they can save 2 or 3 per cent in fuel, or more if you spend more time in thick city traffic. Stop-start is mainly in German brands for now - including BMW, Porsche and Audi - but expect to see it on most new cars by about 2015 as manufacturers ramp up efforts to reduce fuel use.

Automatic headlights

When driving in low-light situations, the vehicle's headlights will be switched on automatically. Variants of the name of this technology include 'dusk-sensing' headlights, or 'light-sensing' headlights. They are marketed as a safety feature, as they allow the driver to concentrate more fully on driving the car. They're particularly handy in Europe, where tunnels often aren't well lit and authorities require headlights to be used. But they can also be handy in Australian tunnels or carparks.

Automatic windscreen wipers

Designed to activate automatically when rain, snow, sleet or any other debris (like Australia's infamous insects) auto wipers can leave you focusing more on driving rather than adjusting the wiper speed. The system is aimed at maximising visibility at all times without driver intervention. The system acts by both activating and altering the speed and rate of the movements of the car's windscreen wiper blades. French cars, including Peugeots and Citroens, use the technology extensively, while most high-end luxury cars are also fitted with auto (or rain sensing) wipers. As with many gadgets, they're not always as intuitive as a human, sometimes leaving the screen wiping longer than most people would.

A flat or Boxer engine is one in which the pistons are horizontally opposed, with pairs of cylinders on the left and the right. It's similar to a V-shaped engine but the V is flat, or 180 degree; hence they're often referred to as a flat-four-cylinder or a flat-six. It has also been nicknamed a Boxer engine because as each piston moves, the piston horizontally opposite to it is exactly counterbalanced in its movement, giving the look of a boxer punching. Some notable Boxer engined brands include Subaru and Porsche.

Bluetooth

Bluetooth is a brand name and a way of wirelessly connecting devices which allows the devices to communicate with each other. Some car audio systems make it possible for mobile phones or iPods to wirelessly link up to the cars controls, allowing the user to make/receive calls and send/receive text messages using buttons on the steering wheel. Some iPods, including the iPhone, can also stream music through the Bluetooth connection. With stricter mobile phone in-car usage laws, it is predicted that this technology will become more readily available.

Body roll

Not to be confused with a roll-over, this basically describes the amount a vehicle leans on its suspension though a corner. Usually the higher a vehicle's centre of mass and the softer its suspension, the more body roll it exhibits. So a 4WD wagon will have a lot, a formula one race car only a little. In large amounts it can feel eerie without necessarily changing a car's handling ability, but depending on the suspension set-up there can be some associated and unwanted steering effects.

Brake assist

An extension of anti-lock braking technology pioneered, as with many safety systems, by Mercedes-Benz. Brake assist basically takes over control of heavy braking when sensors determine the driver wants to stop the car as suddenly as possible. Rather than letting the driver perhaps apply too little brake-pedal force, the computer electronically stomps the pedal for the shortest possible braking distance.

Build plate

A small under-bonnet plaque stamped with the month and year a car left the production line. All cars sold in Australia also have a compliance plate, which certifies when they were released from bond and verified for sale. The compliance plate will always have a later date than the build plate. While it's legal to advertise a car's age on its compliance plate date, the industry will value it off on when it was built. If you're looking to buy a new car early in the year, check what year model it is. One from the previous year should be offered at a discount to the current year.

By-wire

Replacing mechanical components with electronic ones is the Holy Grail of car manufacturers usually because it saves weight, and they can be controlled more easily by a computer. So the throttle cable is gradually disappearing, and one electronically connected to the accelerator is taking its place. Bulky brake boosters will be the next to go in brake-by-wire applications, although issues with reliability means they are still some way off replacing traditional brake systems (Mercedes has used brake-by-wire but kept a traditional brake system as a back-up). Steer-by-wire will remove mechanical steering columns that are dangerous in a crash, and allow more design freedom for steering wheel placement in the cabin.

A canister attached to a car's exhaust system containing a catalyst that achieves the speedy conversion of noxious exhaust gasses into less harmful ones. Because the catalyst is "poisoned" by the presence of lead, the mandatory fitment of catalytic converters in 1986 also meant new cars needed to run on unleaded fuel.

cD (co-efficient of drag)

No, it's not the latest Anthrax album, but what is known as the coefficient of drag. Basically, a cD factor is a number that expresses how aerodynamic a car is as tested in a wind tunnel. The lower the number (around 0.30 is pretty good) the more slippery a car's shape, and amazingly small details such as the shape of a wing mirror or even the design of an exhaust system can make all the difference to fuel economy at higher speeds. That's not the end of the story, however, because to measure true drag the cD must be multiplied by the frontal area of the vehicle. So a small car with an average cD is can more aerodynamically efficient than a big car with a good one.

Close ratio gearbox

Grouping gear ratios closer together can make better use of available engine power by offering less of a gap between each gear. It's not a bad idea for sports cars that are driven hard or engines with poor flexibility low in their rev range, aiding acceleration and hiding gaps in the power delivery. Lower gearing can also mean a lower top speed (not a problem for most of us) but also gives poorer fuel economy because the engine is spinning (revving) faster.

Clutch

Ever wondered what happens when you push that left pedal to change gears? A clutch is basically two plates pressed together between the car's engine and the gearbox. Drive from the engine needs to be disconnected so the gearbox can change gears, so pushing the pedal separates the clutch's two plates, lifting the pedal presses them together again.

Clutchless manual

A misnomer of sorts that refers to a manual gearbox with a clutch engaged by electronics and not a pedal. The driver gets to change gear by a sequential shift (going up and down through the ratios rather than directly to the one needed) via either a push-pull gearstick or steering wheel-mounted controls. Examples are Alfa Romeo's Selespeed and BMW's SMG systems.

Common rail

Common rail is a technology most commonly utilised in diesel engines but also starting to be used in the latest breed of direct injection petrol engines. Instead of individual injectors on each cylinder there is a single high pressure fuel rail. The advantage is a more precise fuel mix and better efficiency, which means more power and lower fuel consumption. Common rail engines can also use precise fuel injection and pre-charge injection to reduce engine noise, making diesels quieter and more refined. The technology has been a major part of the significantly improved refinement and performance in diesel engines in the early 21st century.

Carbon dioxide (CO2)

CO2 is the chemical symbol for carbon dioxide, which is a gas made up of molecules of one carbon atom and two oxygen atoms. CO2 is more commonly known as the greenhouse gas because it is generally regarded as the cause for global warming. Hence the focus on CO2 emissions for vehicles, which account for about 14 per cent of all the CO2 produced in Australia (industry and agriculture are big CO2 emitters). CO2 emissions are directly related to how much fuel a vehicle uses; each litre of fuel emits a certain amount of CO2. Each litre of diesel burnt emits about 2.7kg of CO2, each litre of petrol about 2.3kg and each litre of LPG about 1.5kg. So if diesel produces the most CO2, why are car makers pushing its CO2 advantages so heavily? That's because diesel cars typically use about 25 per cent less fuel, which means that overall diesels generally produce less CO2 than a similarly-performing petrol engine.

Compliance plate

A small under-bonnet plaque stamped with the month and year a car was released from bond and certified for sale in Australia. All cars also have a build plate, which signifies the month and year it rolled off the production line. The compliance plate will always have a later date than the build plate. While it's legal to advertise a car's age on its compliance plate date, the industry will value it off on when it was built. If you're looking to buy a new car early in the year, check what year model it is. One from the previous year should be offered at a discount to the current year.

CVT - Constantly Variable Transmission

A CVT transmission is one that changes steplessly through an infinite number of effective gear ratios. Traditional automatic transmissions only allow particular gear ratios to be selected. CVT can constantly change the engine speed relative to the car speed, which in turn allows the engine to run at its most efficient revolutions per minute (RPM). Some examples of cars currently on the market that are fitted with Constantly Variable Transmissions include Mitsubishi's Lancer and Nissan's Maxima.

Cylinders

Not actual engine components, but a mechanical sub-system of an engine compromising the piston and the cylindrical hole it moves in. Generally, the more cylinders an engine has the more power it develops and the more fuel it uses, but that's also dependent on the state of tuning, and the capacity of each cylinder.

Commonly called a shock absorber, although that's not really correct because in a car's suspension it is actually the spring that absorbs the shock of a bump. The damper is a gas- or fluid-filled tube that controls the movement of the spring and suspension, returning it to its original position. Correct damping is critical to the way a car rides and handles.

Daytime Running Lights

These lights, made popular by Audi, are a proven way of effectively reducing the instance of daytime collisions, particularly between cars and pedestrians. The lights, which are specifically designed to be brighter than standard low-beam headlights, stay on during the day with the aim of increased visibility. Audi uses LED (Light Emitting Diode) technology, which are both more efficient than the traditional headlights, whilst also extending the lifespan of the headlights.

Diesel particulate filter

A diesel particulate filter, or DPF, is part of the exhaust system of many modern diesel engines and is used to remove particulates (including much of the visible black smoke that belches out the tailpipe of some diesels). Particulate filters do a good job of removing much cancer-causing particulates and are now mandatory in some markets, especially in Europe. In Australia particulate filters are optional and many popular makes don't bother fitting them due to the additional cost (estimated at about $1000). However, diesel particulate filters are not for everyone. The DPF is a self-cleaning filter that needs the exhaust system to reach its normal operating temperature for an extended period to achieve this. The only way to do that is to drive the car for some time, usually about 30 minutes along a freeway. That's why modern diesels with particulate filters don't suit people doing short trips around town.

Diff lock

Before electronic traction control the best device for increasing a 4WD's traction in really slippery conditions was a locking differential. As its name suggests it locks the differential, meaning there is effectively a single axle sending exactly the same drive to the left and right wheel (or, in the case of a centre diff lock, the same drive to the front two wheels and the rear two wheels). It's very useful during serious off-roading, where one wheel may lose traction; without a diff lock (or limited slip differential) the wheel would spin almost uncontrollable, potentially leaving you bogged. A diff lock basically ensures equal amounts of torque go to both wheels on the one axle or, in extreme circumstances, all four. Great in tricky conditions, and available on the more hard core 4WDs.

Direct injection

Direct injection is a more efficient way of injecting fuel into the cylinders. It refers to the process of squirting fuel directly into the combustion chamber of an engine instead of first mixing the fuel with air in the inlet manifold. Direct injection technology was originally popularised in diesel engines but is becoming more common in petrol engines as car makers aim to produce more power using less fuel.

Disc brakes

Now the most common type of braking system used but once quite a rarity from when Jaguar pioneered discs on its 1950s Le Mans winning cars. Basically a disc of steel spins on the wheel hub, and is grabbed by calipers wearing heat resistant pads to slow the vehicle down. Front-wheel discs that do most of the work are often ventilated for better dissipation of the heat created by transfer of the vehicle's kinetic energy.

Downforce

Not something the average driver needs to know about, but the Holy Grail of specialist race car engineers called aerodynamicists. Think of an aeroplane's wing that gives it lift. Turn it upside down and you get downforce, which virtually sucks a race car onto the road and improves the amount of tyre grip through corners.

Dry weight

The dry weight of a vehicle refers to the car's weight minus its fluids, including fuel, oil and coolant. It's largely irrelevant because no car will ever be driven like that. A more accurate measure of vehicle weight - which impacts fuel consumption - is kerb weight, or how much the car weighs when driven.

Dual clutch transmission (or twin-clutch transmission)

Dual clutch transmissions have become increasingly common thanks to potential benefits in efficiency and performance.

To the driver they operate like a regular automatic - with two pedals and a gear selector - but underneath they are effectively a manual gearbox with two computer-controlled clutches.

As with conventional automatic cars, vehicles fitted with a dual clutch transmission have just two pedals used for braking and acceleration. Each of the clutches looks after half the geabox; the first clutch, for example, will select first, third, fifth and seventh gears, while the second will select second, fourth and sixth gears.

The reason for the two clutches is so that one can be pre-selected in the next tallest gear. When the car changes up a gear it's effectively changing clutches, not gears.

The result is a gear change that is usually significantly quicker than any traditional automatic or manual transmission. The gearshifts can also be super smooth.

The downside is that some dual clutch transmissions can be jerky or hesitant at low speed. Many also don't have the traditional tendency of an automatic to roll forward when stationery, instead having a hill hold system to stop the car rolling back.

First introduced locally in the original Audi TT V6, dual clutch transmissions are now used in all manner of cars ranging from the Ford Fiesta to the Ferrari 458 Italia.

Colloquial term for a transversely mounted engine; that is, one aligned so the crankshaft is perpendicular to the car's central axis. It is a useful layout for front-drive cars where the engine sits between the driven wheels, and major transmission components line-up nicely. The same goes for mid-engined rear-drive cars, although in racing cars aerodynamic considerations result in a longitudinal - or north-south - configuration.

Electronic brakeforce distribution (EBD)

This system automatically varies the force applied to each of a vehicle's individual brakes based on road conditions, vehicle speed, and vehicle loading. It is invariably coupled with an anti-lock braking system, and by applying more or less pressure to each wheel, it allows for greater control in the event of heavy pressure being applied to the brake pedal. It can also help with brake wear by diverting more braking power to the rear wheels in non-emergency situations (the front wheels of any vehicle do the majority of the braking). EV, or electric vehicle

Expect to hear more about EVs over the next few years as manufacturers work on vehicles that have no harmful emissions. As its name suggests, an electronic vehicle is a car that runs solely on electricity, generally able to be charged through a regular household powerpoint. Some can also be charged through higher-power industrial powerpoints for a faster charge, something that is seen as a negative to EVs. Mitsubishi is the first car maker to offer an EV in Australia with its i-MiEV, although it's set to be very expensive and only available to a select few. Most car makers are working on EVs, including Mini, Volvo, Smart, Nissan and Subaru.

Electronic stability control (ESC, ESP, DSC or VSC)

It seems every manufacturer has its own acronym (such as DSC, VSC or ESP) to describe similar electronic systems that help stop a car sliding sideways through a corner. A complex array of sensors monitor wheel slippage, steering angles and the car's amount of yaw to intervene automatically using the brakes and reduced engine power. ESC systems can do something even the world's best drivers can't - individually apply braking to one or more wheels in order to control a slide. Hopefully you'll never need it, but it's one of those things that can - literally - work wonders in avoiding a crash. As with other safety systems, though, the laws of physics still apply, so if there's not enough grip (or enough road) a crash is still very much a possibility.

Emissions

Vehicles powered by fossil fuels emit a range of often harmful gases into the environment. Reducing these emissions is high on the agenda of governments and car manufacturers around the world as they try to reduce the environmental impact of vehicles.

Forced Induction is an air intake system that allows the air/fuel mixture to enter the combustion chamber at a higher than atmospheric pressure. Effectively, air is forced into the combustion chamber the more air you can shove into each cylinder, the more fuel you can add. That means a bigger bang and more power. The two most commonly used technologies of forced induction are superchargers and turbochargers. Both are effectively giant air pumps, with the supercharger run directly off the engine and a turbocharger using the exhaust gas pressure. Four-stroke engine

The staple configuration of virtually every piston car engine. As each piston goes up and down there are four stages in the process: intake, where combustible gasses are sucked in; compression, where the gasses are squeezed before combustion; the actual combustion of the mixture, and then exhaust as the burnt gasses are forced out again.

Front-wheel drive

The driven wheels are the ones the engine turns, which makes the car go. In this case, it's the front wheels - currently a popular choice among car-maker because it packages all the major mechanicals in the one place near the engine to reduce manufacturing costs and help with efficient use of space. It also means you don't have to run a drive shaft down the length of the car, which can add weight and take up valuable underfloor space.

Fuel Cell

A fuel cell is a device that conducts a chemical reaction to produce electricity, usually from hydrogen. The best way of describing a fuel cell is to consider a hydrogen fuel cell powered vehicle: the fuel cell uses an electrochemical process to convert the chemicals hydrogen and oxygen into water, and in the process it produces electricity. In this sense, it works similarly to a battery-however the fuel cell never needs to be replaced; only the fuel that it uses to create electricity.

Fuel consumption (L/100km)

The official fuel-consumption figures are conducted according to a government standard known as ADR 81/02 (ADR referring to the Australian Design Rules that govern all new cars sold here). It is made up of two main drive cycles designed to replicate city and country driving - urban (city) and extra urban (country, or freeway). All testing is conducted in a laboratory (with the temperature between 20 degrees and 30 degrees) but takes into account the aerodynamic efficiency of the vehicle and its weight. The urban test involves a 13-minute series of stop-start procedures with the vehicle travelling at up to 50km/h (the car is actually stopped for a total of four minutes during the 13-minute cycle). The extra-urban cycle involves the car accelerating from a standstill and holding various speeds up to 120km/h. Even in the extra-urban test cycle - which lasts for six minutes and 40 seconds - the car is stopped for a total of 40 seconds. A formula is then used to calculate a combined average fuel economy that's supposed to be indicative of what you can expect to use in average vehicle use. In reality, though, most cars will use more and the combined figure published on every new vehicle's windscreen should only be used as a comparative guide. In recent years many car companies have also become more savvy with making their vehicles perform better in the test than it may in real life. To check the urban and extra-urban figures for your car, go to greenvehicleguide.gov.au.

The first automotive head-up display occurred in the 1990s in a Nissan Bluebird and the basic concept hasn't changed since then, although the technology tends to be reserved for more expensive luxury cars these days (BMW and Lexus are leading the way in employing the technology). A HUD projects information on to a virtual point at the end of the bonnet, meaning drivers don't have to take their eyes off the road to view key information such as speed, engine warning lights or satellite-navigation commands. The HUD can generally be disabled at the driver's discretion.

Heel and toe

Keen drivers like to blip the throttle when changing down a gear in a manual to match engine revs before the lower gear is engaged. If both feet are being used on the brake and clutch pedal, the right foot needs to be rolled across to give the throttle a stab. So it's toes on the brake, heel on the accelerator, or more likely, the side of the foot, unless the driver is double jointed.

Hill hold

Hill hold systems temporarily hold the brakes when conducting a hill start, meaning the driver doesn't have to worry about using the handbrake. When the car is in gear, this allows the right foot to move from the brake to the accelerator, without the need for the handbrake to be applied. They automatically disengage after a few seconds (in case you want to roll backwards on purpose) or when the clutch is engaged. More recently hill hold functions have been added to automatic cars - especially various Audis and Volkswagens with a twin-clutch auto and push-button park brake - to make city driving more friendly.

Hybrid system

A fuel-saving powertrain that combines a small petrol or diesel engine with an electric motor is called a hybrid. The engine drives the car's wheels while charging a battery so the motor can do some of the work. The electric motor can also run the car on its own for short distances, allowing the petrol engine to be temporarily switched off. Hybrids also use regenerative braking, whereby energy normally lost in heat during braking is transferred back into electricity. It's expensive technology and far from the final word in alternative energy sources; hybrids offer their best benefits during stop-start traffic (city driving) so the benefits are almost entirely lost on a freeway. Only a handful of cars in Australia - the most common being the Toyota Prius - currently uses a hybrid powertrain. The next breed of hybrid vehicles are called plug-in hybrids; as the name suggests they can be plugged in to a powerpoint to recharge their batteries.

Invented by BMW, this system is aimed at reducing clutter on interior dashboard surfaces by replacing buttons with a central control wheel. The wheel is used to navigate through menus on the display screen on the dash. iDrive-like controllers is a term that is now used to describe other similar systems from the likes of Audi, Mercedes-Benz and Lexus.

Intercooler

A device used on turbo or supercharged engines to increase horsepower. Basically, cooler air is denser, and contains more oxygen for the engine to burn. An intercooler works a little like a radiator and is usually placed at bumper level at the front of the engine or, as in a Subaru WRX, under a big bonnet scoop. By dropping inlet temperatures it helps power output and also engine longevity.

IRS

Stands for independent rear suspension, meaning a car's back wheels are hinged independently so they can move up and down without affecting each other. Compared with a live rear axle - basically a solid beam containing the differential and drive shafts in a rear-drive car - it can give more accurate handling over bumpy roads and better grip by working more effectively at keeping the tyres in contact with the road.

Kerb weight refers to the weight of the car as it is driven. As well as the weight of the vehicle the measurement generally includes almost a tank of fuel (90 per cent) while some car maker also factor in the weight of a 68kg driver as well as 7 kg of cargo.

Kilowatts

A metric unit used to measure power - in this case, the rate at which a car's engine turns the energy stored in fossil fuels into movement. Usually, the more kilowatts an engine produces, the faster a car will accelerate. One kilowatt is equivalent to 1.341 brake horsepower, although many people like to use the latter measurement because it sounds tougher and less clinical.

These lights are more efficient than traditional bulbs, which means they use less energy, in turn saving fuel (albeit only in tiny amounts). LEDs also typically last the life of the car, which means they're less likely to fail, bringing an obvious safety benefit. Another area they boost safety is by illuminating quicker than conventional filament light globes; LEDs can illuminate about 200 milliseconds faster than conventional bulbs, which is about 5 metres if your car is travelling at 100km/h.

Low profile tyres

The aspect ratio of a car's tyre is the height of the sidewall between the wheel and the road, and is expressed as a percentage of the tyre's width. So a normal passenger car might have a 205/65 (width/sidewall height) tyre, with plenty of cushioning effect for a better ride. A low profile - say, 245/45 - tyre on a sports car has a narrower sidewall with less flex for more accurate handling.

Low-range gears/transfer case

Good off-road vehicles should have low range gears that act almost as a second gearbox to keep engine revs higher for a given road speed. It means there's more engine braking going downhill when touching the brakes would be dangerous, and more engine power available at low speeds heading uphill.

Most cars have their engines under a conventional bonnet, but some have them mounted behind the driver. If it is also ahead of the rear axle, it called a mid-engined layout because that's the best place to achieve the right balance for high-performance handling. Basically, a mid-engine layout is any layout where the engine sits between the front and rear wheels, rather than over the front wheels (as with most vehicles) or behind the back wheels (as with Porsches 911s and the old Volkswagen Beetles). Virtually every purpose-built race car is mid-engined, and quite a few production sports cars.

Monocoque chassis

In the old days cars used to have a rugged, truck-like chassis that contained the suspension and engine, onto which was bolted a separate body. Every car (apart from a few 4WDs) now has a monocoque, which is basically a rigid, complex box with mechanical components bolted directly underneath.

Multi-valve

Engines need to breathe air, and usually the more they can get the more efficiently they operate. So instead of each cylinder having two valves (one to suck gasses in, another to blow them out) adding an extra pair means designers can make better use of the shape of the combustion chamber for intake and exhaust. A four valves per-cylinder configuration was once rare, but is now normal (some high performance engines have even used five valves per-cylinder). Most manufacturers now use a "multi-valve" configuration, and it also gives the marketing men another high-tech term to sell off.

A simple enough acronym that stands for noise, vibration and harshness, but a nightmare for designers looking for a quiet and civilised car. It encompasses everything from transmitted wind, road and engine noise to rattles in the body, vibrations from the engine and transmission to secondary harmonics caused by the whole lot. Inevitably, once one noise is reduced, it reveals another that couldn't be previously heard. Lexus owners probably don't know what we're talking about.

Octane rating / RON

Often misunderstood as an energy rating of petrol, octane ratings instead refer to how stable the fuel is and, therefore, how it can be used.

Octanes are hydrocarbons, part of the chemicals present in fuel that give the product its energy.

Petrol engines compress fuel before spark plugs burn it, though fuel can ignite at the wrong time. Mis-ignition, described as “pinging” or pre-ignition, can be caused by heat and compression, and lead to potential engine damage.

RON stands for Research Octane Number, a figure that reflects how fuel burns in a controlled manner and how resistant it is to mis-ignition.

Fuels with a high octane number are less likely to combust at the wrong time, making them more ideal for use in engines with a higher compression ratio (which allows more air into the combustion chamber). That typically means ultra-efficient or high-performance motors that place more demands on fuel.

Standard 91 octane petrol is more likely to mis-ignite in harsh conditions than 98 octane premium fuel. Many modern engines detect what sort of fuel is being used and make small changes (to ignition timing, for example) to capitalise on high octane fuels, which can .

This really refers to the camshaft, or the rotating shaft covered in bumps - or cams - that open and close an engine's inlet and exhaust valves. Older style engines had their camshaft built into the block, from where the valves were operated by pushrods. Placing them in the cylinder heads, or "overhead" is a more efficient method of valve operation. If there's two, you've got a double overhead camshaft or DOHC. But don't be confused by so-called quad-cam systems. They refer to a DOHC system on a car with two banks of cylinders (like a V6, for example) so offer no advantage over a DOHC system in a car with only one bank of cylinders.

Oversteer

Literally, this means the car turns into a corner more than what the driver intended, but how does that happen? It is the result of a lateral rear-wheel skid that brings the back of the car around, or in other words the rear tyres slide sideways. Oversteer might be caused by the application of too much power in a rear-drive car, backing off the power on a slippery road, or simply poor handling balance or worn rear tyres. Skilful drivers can apply steering in the other direction (opposite lock), which can help control the slide. Heavy braking can sometimes make the situation worse.

Previously only available on expensive luxury cars, park assist systems are filtering down to relatively affordable transport like the latest Commodores and Falcons. Basic systems incorporate proximity sensors in the rear bumpers and audible warnings when you're backing too close to a solid object. More complex units have flashing lights and different sounds for different corners of the car and, thankfully, an on-off switch.

Plug-in hybrid

A plug-in hybrid is effectively an electric vehicle with a small petrol or diesel engine acting as a generator to recharge its batteries. As the name suggests, a plug-in hybrid car can also be plugged in to a regular power point to be recharged. The beauty of a plug-in hybrid is that it also has the regular engine acting as a back-up generator. When the batteries of a plug-in hybrid start running low the engine starts up and starts charging the batteries. Unlike a regular hybrid vehicle the engine of some plug-in hybrid vehicles never actually drives the wheels. Instead it's purely a generator used to charge the batteries which, in turn, power the electric motor/s. An example of this kind of plug-in hybrid is the Chevrolet/Holden Volt. A different type of plug-in hybrid is the upcoming Volvo XC70 Hybrid, the engine of which will drive the wheels.

Power to weight ratio

A simple formula comparing how much power a car's engine delivers with how much the car itself weighs and usually expressed in kilograms per kilowatt. Less weight means more acceleration so, for instance, a Lamborghini Gallardo with a low power to weight ratio is going to smoke a Land Rover Discovery diesel (with a high power-to-weight ratio) on the drag strip.

Premium unleaded petrol (PULP)

Premium unleaded fuels have higher octane ratings and are more stable than regular petrol. Regular 91 octane fuel is more likely to mis-ignite and cause engine damage than than 95 or 98 octane fuels. Some cars are designed to use 95 or 98 RON premium fuels and could be damaged by low octane fuel.

All modern cars that require premium unleaded have it listed in the owner's manual as well as on the inside of the fuel filler flap. Often they will have a sticker saying something like "Minimum 95 RON" or "98+ RON".

Many premium fuels including the Caltex Vortex line feature detergents that can clean engines and reduce carbon buildup, helping protect engines in the long run.

Quite simply stands for "revs per minute" and in automotive terms refers to how fast an engine's crankshaft is spinning. Most will idle at about 800rpm and spin to a maximum of around 6000rpm, but a Formula One engine can pull more than 18,000rpm. If that doesn't sound impressive, try cranking an egg beater 300 times every second; then you'll understand why F1 engines can be fragile.

A complex and expensive replacement for the street directory, now available in many cars. Satellites track the position of the car, the information is related to maps on CD or DVD ROMS, and a little TV screen tells the driver where he or she is, or where to go. Expect to pay around $5000 for the privilege. Aftermarket systems (which can be affixed to the windscreen with suction cups) are also popular these days and sell for less than $500.

Springs

A car contains plenty of springs: in the doors, the bootlid and engine valves to name a few. But usually, they're the ones in the suspension that these days are invariably coil springs. They absorb the travel of a wheel as it goes over a bump and the damper returns the wheel to its original position. Some commercial vehicles still use leaf springs, which replace a coil with a series of steel leafs bound together then bowed (or curved) to suspend the vehicle.

Smart Key

A 'smart' key (also marketed as Keyless Entry, Keyless Go or Passive Go) is a system that allows the driver to keep the key in their pocket and simply press a button to start the car. The car can automatically detect the presence of the smart key via a transponder unit, enabling the start button. Many smart keys also allow you to unlock the doors without having to fumble for keys in your pocket. Once the key is detected within about one metre of the car it allows you to simply open the door handle. There are obvious benefits, although one downside is if you accidentally get out of the car and hand the driving duties to a friend (most cars will warn that the key has left the vehicle, but it is still possible to drive off). It's also possible to lose the keys down the side of the seat or somewhere else in the car, at which point anyone can theoretically take the car. Smart keys always have a regular metal key embedded in them to allow you to at least open the doors mechanically should the electronics fail.

SRS airbags

We all have an image of airbags being soft, billowy pillows that save our lives in accidents, but have a think about this little experiment. Have someone hold a pillow against your bedroom wall and then run full tilt at it - that's about 25km/h for a self-propelled human - and smash your face into the pillow. Double the pain the injury if the speed was 50km/h. That's about how much effect an airbag has in a car crash if a seatbelt hasn't already slowed your progress - and who drives at 50km/h anyway? So an airbag is a Supplementary Restraint System, not a replacement for seatbelts or deformable structures in cars.

Supercharger

A supercharger is basically a big mechanical air pump. It's trying to achieve the same goal as a turbo - pump more air into the engine, which in turn allows more fuel to be added to the engine, resulting in more power. Attached to the engine, a supercharger uses some of the engine's power to operate. But it produces much more power in the process (using more fuel along the way). Superchargers can add significant increases in power. While they use more energy to operate than a turbo, the fact they're running directly off the engine means it operates as soon as the engine starts spinning, so there's no lag.

Torque is best considered as the measurement of power that gets you moving, whereas power is the measurement of how fast torque is being used. So should torque be an important figure to a new car buyer? Well, torque measures the twisting force created in an engine, which means it is critical if you need quick acceleration power. In layman's terms, torque is the meaty mid-range response that gives strong pull at lower engine revs, making the car more relaxed to drive around town and reducing the need to change down to lower gears. Torque is also crucial for towing, which is why turbo-diesel engines (typically with loads of torque) make such good towing companions. Engines with high levels of torque typically have larger capacities (engine capacity is measured in litres). Turbochargers and superchargers can also significantly boost torque.

Tiptronic

A type of automatic gearbox operation pioneered by Porsche that allows a degree of manual over ride by the driver for better control of gear selection. Although still a normal self-shifting auto, the Tiptronic gearbox also has a separate gate or steering wheel-mounted buttons to allow sequential selection of a desired gear ratio.

Torque steer

In front-wheel drive cars the driven wheels also do the steering, so as power is applied the driver feels a torque reaction back through the steering wheel. This may vary from a slight stiffening of the steering to an actual change of intended direction in high-powered front-drivers.

Traction control

This is an electronic system designed to stop a car's driven wheels (either front, rear or all) from spinning. Sensors at the wheels tell a microprocessor if it is spinning too fast, and either a brake is applied or engine power reduced to bring it back into line. It's handy on slippery roads to move away from standstill, and can also reduce unwanted lateral movement if too much power is applied though a corner.

Transmission

We usually call a gearbox - the set of cogs used to lever a car along at different speeds - by this name, but it really refers to the entire system that transmits engine power to the road wheels. So it includes the gearbox (whether automatic or manual) driveshafts, differential and any tail shafts needed in rear- or four-wheel drive cars.

Turbo

A term used for adding excitement to everything from Bentleys to vacuum cleaners, but in an automotive sense the turbocharger basically provides more engine power. A turbo is a kind of pump that forces more air into an engine, and because it is driven by the engine's exhaust it is a good source of 'free' power. The more air forced into an engine the more fuel you can add as well, which is where the power comes from. A turbo can give a small capacity engine much more grunt. The downside is fuel consumption is almost always higher, and some of the engine's flexibility can be lost as the turbo gets up to speed, which is known as turbo lag.

Two-stroke engine

A more simple engine configuration then a four-stroke, with two elegant cycles of combustion and exhaust. Two stroke engines require far fewer moving parts and so are good for compact layouts needed in lawn trimmers, outboard boat engines and motorcycles. Power tends to be limited to a narrow band, however, making them less suitable for heavy vehicles such as cars. They are often also not as clean in their operation as a four-stroke engine.

Not surprisingly, this is the opposite of oversteer and means a car turns into a corner to a lesser degree than the driver intended. In other words, you turn the steering wheel and the car keeps going straight ahead as the front wheels slide across the road surface. It's usually more pronounced in front-drive and all-wheel drive cars with an unhealthy forward weight bias but is also common in rear-drive cars. Manufacturers often tune a car's handling to exhibit understeer, believing it to be safer because a driver will naturally back off the throttle, which usually brings the car back into line.

USB input port

This port aims at making connectivity with an MP3 player simple, by allowing the device to be plugged directly into the stereo of the car via a USB (universal serial bus) cable that's now commonplace on computers and myriad electrical components. Much less clutter than carrying around 50 of your favourite CDs, this technology is becoming more widely available, with many new cars as well as aftermarket stereo systems offering USB connectivity. A USB interface also usually allows the song lists and track details to be relayed to the vehicle's digital display.

Voice control is another safety measure that aims at giving the driver less to be distracted by. The system, which is available in cars such as Ford's Mondeo - and most luxury cars - allows the driver to choose CD tracks by number, as well as adjusting the in-car temperature just by saying: 'temperature' then the desired level, eg '22'. Most cars repeat the command made back to the driver through the stereo system.

Weight distribution is generally explained as a ratio of weight over the front wheels compared with weight over the rear wheels. For example, the weight distribution of the Mercedes SLS AMG Gullwing is 47:53, which is considered perfect for the layout of the car. The distribution of weight in a car is directly related to the way the car will behave through its acceleration, handling, balance and component lifespan. Manufacturers often aim for what's often described as a "perfect" 50:50 weight balance, because the car will feel neutral in corners. Most cars have more weight over the front wheels because heavy mechanical components such as the engine and gearbox are positioned towards the front of the car, in some cases giving the car a nose-heavy feel, especially when driven enthusiastically. Other cars, such as the rear-engined Porsche 911, have more weight over the back wheels, requiring a different driving style. Formula One cars also have more weight over the rear wheels due to the engine sitting behind the driver.

Wheelbase

This is a measurement between the centre point of a car's front and rear wheels. Why is it important? Mainly because it can determine the amount of interior room in a car, in that a longer wheelbase means more space for seating. Short wheelbase cars can be more nimble and manoeuvrable, but can pitch over bumps and be less stable. Wings and spoilers

Not surprisingly, these are aerodynamic devices used in high performance and race cars to direct air flow over a car's body to push the car down onto the road - much like an aircraft's wing, only with the reverse effect. They also give more mundane cars a sporty look. Because they only work at high speed wings and spoilers on road cars are mainly for cosmetic purposes only. And as a grab handle to shut a boot lid.

Xenon is a type of gas used in light bulbs that creates a much more pure bright light than traditional filament bulbs. They also last longer, and use less energy, in turn reducing the load on the electrical system and saving some fuel. Bi-Xenon headlights use a single xenon bulb unit for both high and low beam. Xenon lights are generally more expensive than regular headlight units - often costing thousands of dollars for a single headlight - which can prove costly in the event of a minor crash.